Evidence demonstrates that taurine, present in high concentrations in the vertebrate retina, is an essential amino acid for the integrity of visual structures. Depletion of taurine in both animals and man has resulted in electrophysiologic and morphologic abnormalities. There is little information as how taruine is functioning at the molecular level. Thus, this proposal will address the following hypotheses: 1) that taurine produces changes in retinal proteins at the molecular level, and 2) that the effects of taurine on calcium ion uptake in the retina are related to the effects of taurine on protein phosphorylation. In previous studies from this laboratory it was reported that taurine inhibits the phosphorylation of specific retinal proteins. The animal tissue to be used in the experiments will be the rat retina. Two preparations of rat retina will be utilized: 1) a crude retinal homogenate, and 2) a P1 fraction which contains photoreceptor cell synaptosomes prepared by differential centrifugations in sucrose. Specific aims will be to investigate the influence of taurine and taurine analogues on calcium ion uptake and protein phosphorylation at both low (10 MuM) and high (2.5 mM) calcium ion concentrations. The retinal kinase that is inhibited by taurine will be purified and characterized by routine biochemical techniques. The relationship of calcium ion uptake and protein phosphorylation in the taurine-depleted retina will be studied. The animals will be made approximately 70% taurine deficient by treating with guanidinoethanesulfonic acid, a taurine transport inhibitor. Finally, it is proposed to determine the site of the specific protein in the retina whose phosphorylation is inhibited by taurine by isolating and purifying the protein, producing monoclonal antibodies to the protein, and then localizing the protein in the retina by immunohistochemical techniques. The significance of the research will be to determine a function for taurine in the retina at the molecular level. Previous results such as inhibition of protein phosphorylation and alteration of the transition temperatures in Arrhenius plots of calcium ion uptake indicate that taurine is indeed affecting biological processes at the molecular level.